March 21st, 2012, Aim: How do we solve more complex problems ???

 

• Some math problems may be harder to solve and they are called complex problems.But just because their harder to solve, doesn't mean there impossible.

• With solving the area for a circle, it may be harder with the information given like circumference.

• CIRCUMFERENCE is the boundary line of a circle.

The Formula to find the circumference . . .

C=πd

(where c is the circumference and d is the diameter)

Now when it comes to finding the area of a circle and its a complex problem they make ask it like this --->

  "If C=12π, then what is the area ?"

Now when you see that don't panic ! Stay calm !

• You know that the area of a circle is A=πr^2
• And the the circumference is C=πd.

• Half of the d is r, so if d is 12 divide it by 2 to find the radius

Example :

1.  C=12π
2.  12/2 = 6
3.  r=6

• Now that you know r is 6 plug it into the area formula for the circle

Example :

1. A= πr^2
2. A= π6^2
3. A=36π

See its possible to find the answer !

Lets try one more example . . .

 

• If the circumference of a circle is 75πcm, then what is the area ?

1. 75/2= 37.5
2. A=πr^2
3. A= π37.5^2
4. A=1406.25π

THERE'S THE ANSWER ^

 

Now you give it a try !!!

1) If the circumference of a circle is 25π, then is the area is 156.25π?

• yes
• no

2) If the circumference of the circle is 100π, then what is the area ?

1. 2500π
2. 50π
3. 100π 

 ( WRITE ANSWERS IN COMMENTS BELOW ! )

*photos from google*